The present invention relates to a container suitable for the shipment and storage of radioactive isotopes. More specifically, this invention relates to a container comprised of at least one polymer material that is chemically inert, or compatible, with a radioactive isotope therein.
Radioactive isotopes are generally transported within containers designed to ensure containment of the isotope in case of mechanical stress, and typically include shielding to reduce the level of radiation emitting from the container. For example, in U.S. Pat. No. 5,303836, there is disclosed a container suitable for the transport of highly enriched uranium comprising a heavy duty drum with a fiberboard and plywood insulation material, and an inner container made from stainless steel. U.S. Pat. No. 3,769,490 discloses the use of a leaded glass vessel for the transport of Tc-99m. The use of a shielded glass bottle for the storing or shipping radioisotopes is also disclosed in U.S. Pat. No. 3,655,985 and U.S. Pat. No. 4,074,824. U.S. Pat. No. 3,882,315 and U.S. Pat. No. 4,066,909 are also directed to containers for the storage and transport of radioactive isotopes and include embodiments to help absorb spillage, or ensure leak-tight coupling of a cover assembly, respectively. In many applications, radioactive isotopes are shipped in glass, however, in order to ensure that there is no breakage of the glass during shipment, the glass shipping vials are manufactured with very thick walls. As a result, part of the volume of shipping containers is used up by glass and not the desired radioisotope, which leads to increased shipping costs. Furthermore, from a customer standpoint, a major drawback arising from the use of glass is the potential for breakage as the shipping bottles may be subjected to significant mechanical stress at times.
Other material have been used for the shipment of radioisotopes. However, it has been observed that during the storage or shipment of radioactive isotopes, for example, molybdenum-99 (Mo-99), that precipitates of the isotope form over time. The formation of precipitate is especially evident when Mo-99 is shipped in NaOH, which is the preferred solution required by customers. The formation of precipitates concentrates the isotope and radiation within a small area of the container which may result in weakening of the container resulting in susceptibility to brittle fracture and failure of the container from impact. For example, Mo-99 solutions are typically transported within containers comprising high density polyethylene (HDPE). However, high activity or concentrations (.about.10 Ci/mL) of Mo-99, especially in a NaOH matrix, is not stable within HDPE bottles, and precipitates are routinely observed after a few hours following the dispensation of the isotope. A major problem with the precipitation of Mo-99 is that a high concentration of radioactivity accumulates within a small area of the bottle and this causes the structural integrity of the bottle to weaken and periodically fail during shipment, especially during extended shipment times, for example from North America to Japan, Europe or South America. HDPE containers containing Mo-99 have been known to fail after 48 hours shipping. Furthermore, customers do not like the black Mo-99 precipitate within shipping containers due to the additional processing required. A similar problem with other isotopes (such as W-188) in an NaOH matrix may also lead to precipitate formation within HDPE shipping containers.
In order to overcome this problem, Mo-99, is shipped with the addition of a stabilizer in order to help maintain the radioisotope in solution. For example, sodium hypochlorite (NaOCl) is normally added in order to slow down the reducing reaction which causes Mo-99 to precipitate, but some precipitate formation is still observed. The addition of sodium hypochlorite only helps delay the onset of Mo-99 precipitation.
Another problem related to the precipitation problem is gas pressure buildup in the head space at the top of the bottle. Hydrogen build up can occur with the shipment of radioactive isotopes of high activity. Examples of such isotopes include but are not limited to Mo-99, I-131, I-125, W-188 and Cr-51, however, other isotopes that are shipped in large volumes may also produce hydrogen gas over time. The production of hydrogen may be especially problematic with isotopes that do not comprise a "scavenger" for hydrogen, such as I-131 and I-125. Thus there is a need within the art for suitable container materials that are compatible with a radioisotope of interest, and that is suitable for the shipment and storage of radioactive isotopes.
This invention is directed towards providing a container suitable for the shipment and storage of radioactive isotopes, including isotopes wherein precipitation of the isotope may take place, for example Mo-99. In order for a material of a container to be useful for the shipment of isotopes it must be tough, durable, resistant to radiation and chemically compatible with the radioactive solution. Polymers are preferable to glass because they generally have greater mechanical robustness. Preferably, the material is also clear, transparent and mouldable and stable over a large temperature range. The material of the present invention may be used with any suitable container design, as would be known to one of skill in the art.